1. Field of the Invention
This invention relates to a network protector and, more specifically, to a network protector which incorporates a cable trip assembly.
2. Description of the Prior Art
Secondary power distribution networks consist of interlaced grids which are supplied by two or more sources of power so that the loss of a single source of power will not result in an interruption of service. Such networks provide the highest level of reliability possible with conventional power distribution and are normally used to supply high-density load areas such as a section of a city, a large building, or an industrial site. Between the power sources and the network is a transformer and a network protector. The network protector consists of a circuit breaker and a control relay. The circuit breaker includes at least one set of main contacts that move between an open position and a closed position. When the main contacts are closed, electricity may flow through the network protector. The control relay senses the transformer and network voltages and line currents and executes algorithms to initiate breaker tripping or closing action. Trip determination is based on detecting an overcurrent condition or reverse power flow, that is, power flow from the network to the energy source.
Network protectors are often found in dust-proof or moisture-proof housings, or vaults, which are disposed in subterranean passageways in large metropolitan areas. Given their urban, subterranean location, increasing the size of the vault to accommodate larger network protectors is costly and difficult. As such, it is more efficient to reduce the space occupied by certain network protector components so as to allow space for other newer/larger components. That is, by reducing the size of one component or sub-component, another component may be added or an existing component""s size may be increased.
The network protector components, the circuit breaker and the relay, are located within a enclosure within the vault. For safety, the circuit breaker should be tripped before the circuit breaker can be removed form the enclosure. To accomplish this, network protectors include a mechanical trip assembly which is structured to interact with the network protector trip bar. The trip bar is structured to move between a first position and a second position. In the first position, the trip bar prevents the main contacts of the network protector circuit breaker from moving into the closed position. Thus, when the trip bar is in the first position, the contacts are open. In the second position, the trip bar allows the main contacts to be moved into the closed position.
To safely install or remove the circuit breaker from the enclosure, the main contacts must be in the first, open position. To trip the circuit breaker, the trip bar must be moved into the first position. The mechanical trip assembly was structured to be actuated prior to opening the door to the enclosure. Thus, when the door to the enclosure was opened, the mechanical trip assembly, and therefore the trip bar, are in the first position. Thus, before the enclosure is opened, the circuit breaker was tripped. If required, however, it was possible to open the enclosure with the trip bar in the second position, leaving the circuit breaker in the closed position. After maintenance and/or repairs are performed on the circuit breaker or the relay, and after the circuit breaker is installed in the vault, the mechanical trip assembly, and therefore the trip bar, were moved into the second position so that the main contacts could be closed.
As shown in FIGS. 1A and 1B, the prior art mechanical trip assembly 1 included a lever 2, a plurality of rigid members 3, 4 and an end piece 5. The end piece 5 engaged the trip bar 6 on the circuit breaker 7 (shown in part). The mechanical trip assembly 1 and the circuit breaker 7 were both mounted on a frame 8 that was structured to move in and out of the enclosure (not shown). A spring 9 biased the mechanical trip assembly in a first position in which the trip bar 6 was moved into the trip bar first position which tripped the circuit breaker 7.
In operation, when the circuit breaker 7 was in use and disposed within the enclosure, the lever 2 was held at about a 45 degree angle so that the mechanical trip assembly 1 was in a second position holding the trip bar in the second position. Prior to opening the door to the enclosure, a user actuated an external handle (not shown) which was coupled to the lever 2, thereby moving the mechanical trip assembly 1 in to the first position which, in turn, moved the trip bar 6 into the first position causing the circuit breaker 7 to trip. At this point the circuit breaker 7 could be safely removed from the enclosure. After the circuit breaker 7 was returned to the enclosure and the enclosure closed, the procedure for closing the circuit breaker 7 contacts included a step which returned the lever 2 to a 45 degree angle, i.e., the mechanical trip assembly 1 and the trip bar 6 were both moved into their respective second positions thereby allowing the contacts to be closed.
The mechanical trip assembly 1 occupies a certain amount of space within the enclosure. This includes occupying a certain width as best seen in FIG. 1A. If the width and/or size of the mechanical trip assembly 1 could be reduced, the space could be occupied by other sub-components of the network protector. Thus, the network protector could be upgraded without having to reconstruct the enclosure and/or vault. Additionally, mechanical trip assemblies have other disadvantages. For example, if one rigid member 3, 4, or other part failed, the entire assembly would not operate properly. Additionally, manufacturing tolerances at each attachment point between the rigid members, lever, and other parts had a cumulative effect making positioning of the end piece 5 on the trip bar 6 difficult.
There is, therefore, a need for a trip assembly that occupies less room than a mechanical trip assembly.
There is a further need for a trip assembly that has fewer components than a mechanical trip assembly.
There is a further need for a trip assembly that securely engages the trip bar.
These needs, and others, are satisfied by the invention which provides a cable trip assembly. The cable trip assembly includes an actuating assembly, a mounting assembly, and a cable assembly. The cable assembly includes a cable member disposed within a sheath. The cable member has a first end and a second end. The cable member first end is coupled to a lever, which is part of the actuating assembly, which is structured to move between a first position and a second position, similar to the prior art lever. The cable member second end is coupled to the circuit breaker trip bar. The sheath is mounted on a rigid frame, preferably the circuit breaker itself. Thus, with the sheath held stationary, the lever can move the cable within the sheath between a first and second position as the lever moves between its first position and second position. Because the cable member second end is coupled to the circuit breaker trip bar, the trip bar is also moved between the trip bar first and second positions as the lever moves between the lever first position and second position.
The cable trip assembly occupies less space than the prior art mechanical trip assembly. Thus, the space that was previously reserved for the mechanical trip assembly may be utilized by other components or sub-components. Additionally, the cable trip assembly has fewer linkages between the lever and the trip bar and therefore, the aggregate of the manufacturing tolerances for the cable trip assembly is less than the aggregate of the manufacturing tolerances for the mechanical trip assembly.